A calcium-activated cation current by an alternatively spliced form of Trp3 in the heart

To investigate a cDNA encoding cation current, we isolated an alternatively spliced form of a rat Trp3, designated Trp3sv, Trp3sv encodes 736 amino ac ids with a unique N terminus and six transmembrane segments. Expression of the cRNA in Xenopus oocytes was successfully performed. The cation selectiv e current appeared after the addition of ionomycin or induced by prolonged depolarization but not by hyperpolarization. This induction was not observe d by a treatment with thapsigargin, phorbol ester, or ATP, Na+, K+, tetraet hylammonium, and divalent cations were permeable, while N-methyl-glucamine and chloride were nominally impermeable ions, The currents were not inhibit ed by flufenamate ruthenium red but nonspecifically by 2 mM Gd3+. Northern as well as Western blot suggested lower levels of the expression observed i n some organs, while reverse transcriptase-polymerase chain reaction sugges ted that it widely spread among various organs. Therefore, we may conclude that N-terminal spliced valiant of Trp3, Trp3sv, encodes a calcium-activate d cation channel in various organs.